Luciferin potassium salt is a small molecule that consists of a benzothiazole moiety attached to a thiazole carboxylic acid moiety. Luciferin is a natural substrate of luciferase, an enzyme found in Firefly luciferase. This molecule has fluorescent properties (Ex 328 nm; Em 532 nm in H2O)1,2 but it is mainly used for bioluminescent imaging (BLI) purpose.
BLI is a natural process that has been found in various living organisms such as the North American firefly (Photinus pyralis) and is based on the oxidation of D-luciferin catalyzed by the enzyme Luciferase. Upon recognition by the enzyme, D-luciferin is oxidized to oxy-luciferin and releasing one photon of light, which can be detected by a CCD camera (Figure 1). The intensity of the light output is closely related to the amount of D-luciferin available for the enzyme and therefore it is possible to quantify the amount of luciferin by measuring the amount of emitted light with a CCD camera. As a non-invasive imaging method, BLI is comparable to other in vitro and in vivo techniques but has the advantage of high sensitivity, convenience and ease of use. It does not require a light source (as opposed to fluorescence) and there is no background signal from tissues that do not express luciferase. Moreover, it allows real-time imaging of luciferase expressing cells or luciferase expressing mice.3-5 The luciferin/Luciferase process is very substrate dependent and does not allow significant modification on the luciferin scaffold to be recognized by the enzyme.